This application is based on and claims priority from Japanese Application No. HEI 2-126126 filed Nov. 27, 1990, the disclosure of which is incorporated by reference herein.
The present invention relates to a structure of the distal end portion of an endoscope, and more particularly to the structure of a coupling tube located between a distal end body and a bendable portion of an endoscope.
In some electronic endoscopes, a coupling tube is used for coupling a bendable portion and a distal end body containing an objective optical system, in order to accommodate parts such as the solid-state image pick-up element and the like.
In this type of the endoscope, the coupling tube is fitted to the inside, or outside, of the nodal ring of the foremost end of the bendable portion, and fixed by screws or another suitable fixing means.
When the coupling tube is fitted to the outside of the nodal ring, the distal end portion at that location is necessarily increased in diameter. The result is to hinder the smooth insertion of the endoscope into a body cavity and to consequently cause increased discomfort or pain to patients when the endoscope is inserted.
When the coupling tube is fitted to the inside of the nodal ring, the inner diameter of the coupling portion is decreased so as to reduce the space available therein for accommodating contained members, such as tubes and a light guide fiber bundle for illumination. This limits the performance of the endoscope, and attempting to avoid this performance impairment by increasing the diameter of the coupling portion leads to poor insertion of the endoscope and greater discomfort to the patient as discussed above.